The overall objective of our research program is to determine the structure, mechanism of action, biological function, and cellular disposition of certain kidney peptidases. The enzymes under study are the metalloenzyme, renal dipeptidase, and the antidiuretic hormone- inactivating peptidase isolated from renal plasma membranes. Studies on the mechanism of action of renal dipeptidase will include Cl35 NMR analyses of monoanion inhibition, spectral measurements of cobalt renal dipeptidase, characterization of the subunits of renal dipeptidase, and investigation of the association of renal dipeptidase with ribosomes. Using the facile spectrophotometric assay for renal dipeptidase we propose to determine urinary renal dipeptidase levels in urine obtained from patients with various pathological conditions. Isolation and characterization procedures will be employed to study the ADH-inactivating peptidase recently located in plasma membranes of kidney medulla.